1. Field of the Invention
The present invention relates to rapid exchange over-the-wire PTCA balloon catheters, and more particularly, to catheters which are exchangeable over a guidewire.
2. Description of the Prior Art
This description of art is not intended to constitute an admission that any patent, publication or other information referred to is "prior art" with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. .sctn. 1.56(a) exists.
Catheters comprise tube-like members inserted into the body for diagnostic or therapeutic medical reasons. One of the therapeutic procedures applicable to the present invention is known as percutaneous transluminal coronary angioplasty (PTCA). PTCA has evolved through three major stages, fixed wire systems, over-the-wire systems and rapid exchange systems. The first PTCA procedure was developed in approximately 1976-1977 by Dr. Andreas Gruntzig. This fixed wire system featured a core or guidewire fixed within the catheter to stiffen it so that it could be pushed into position in the vascular system. Blockage in a coronary artery could be reduced by positioning the balloon dilatation catheter across from the blockage and inflating the balloon causing the blockage to decrease.
In 1980-1981, Dr. John Simpson began to modify the fixed wire system developing an over-the-wire catheter with a free central lumen for movable guide wires and with a dilatation balloon formed from the outer surface covering in a unitary, that is, one-piece construction. This catheter system is the subject of U.S. Pat. No. 4,323,071. Using such a movable wire system, one could more readily select the desired coronary artery and reach smaller branches as movable guide wires are inherently smaller and more flexible than the fixed wire systems.
If a catheter must be exchanged for one of a different size, the over-the-wire system is advantageous because the guidewire can be left in place. The catheter is withdrawn over the guidewire and another catheter slid into place over it. A disadvantage of this exchange procedure is that it is difficult to keep the guidewire in place, since removing the catheter requires removal of the guidewire and subsequent recrossing of the stenosis. Alternatively a very long "exchange" guidewire of approximately 300 cm can be used. This is difficult to handle because such a procedure requires two operators who must be in communication during the procedure. This requires more time and risks contamination by dropping the guidewire from the sterile field. An alternative to these long exchange guidewires is a two-part guidewire. This is also undesirable because it requires additional time to assemble and may be too thick to allow smooth exchanges.
Rapid exchange catheters were developed to respond to the disadvantage of the long "exchange" wire in over-the-wire systems. These catheters have shorter guidewire lumens passing through the balloon so that the guidewire exits from the catheter closer to the balloon than to the proximal end of the catheter. This enables the physician to anchor or hold the guidewire as he or she removes the catheter from the body with the exchange occurring over the shorter guidewire lumen.
One of the first rapid exchange catheters was U.S. Pat. No. 4,762,129 issued to Bonzel. A disadvantage of this catheter is that the position of the guidewire exit port at the proximal balloon bond coupled with a short guidewire exchange lumen, as in the Bonzel construction, can cause the balloon to become snagged during withdrawal through the tortuous path. The resultant buckling of the catheter may result in inadvertent withdrawal of the guidewire from the lesion due to seizure of the guidewire by the buckled lumen.
Rapid exchange catheter designs such as those in Yock, U.S. Pat. Nos. 5,040,548 and 5,061,273, responded to the problem of catheter buckling and inadvertent guidewire withdrawal by lengthening the guidewire exchange lumen. In Yock, the guidewire lumen passes through the balloon and is generally coaxial with respect to the inflation lumen, but exits (or enters) in the side port at least 10 centimeters from the distal tip of the catheter. The Yock disclosure suggests a lumen of 10 or more centimeters; in catheters on the market, the lumen varies from about 9 to 35 centimeters in length. The lengthened guidewire lumen, however, induces friction between the catheter and guidewire during catheter manipulation and withdrawal. Such friction can contribute to extraneous guidewire movement.
Other versions of rapid exchange catheters are shown in the following patents: U.S. Pat. No. 4,748,982 issued to Horzewski, et al., and U.S. Pat. No. 4,988,356 issued to Crittenden. Here the guidewire lumen contains a slit extending its length (except where it passes through the balloon) so that the guidewire can be removed from the lumen through the slit at a point immediately proximal to the balloon. The lengthened guidewire lumen induces friction between the catheter and guidewire during catheter manipulation and withdrawal. Such friction can contribute to extraneous guidewire movement.
U.S. Pat. No. 4,824,435 to Giesy and U.S. Pat. No. 5,046,497 to Millar represent another variety of catheters, those for instrument delivery. Giesy discloses a method and apparatus for guiding diagnostic and therapeutic devices into tortuous body passages. A secondary guidewire 12 has a guide loop 10 comprising a member which may be threaded over a primary guidewire 14. This allows passage of an instrument over the guidewire 14 without the use of a through-lumen. The guide loop 10 is positioned at the tip or distal end of the instrument. The instrument is advanced alongside the guide wire 14 and is kept on course via the secondary guide wire 12 pushing behind the instrument.
U.S. Pat. No. 5,046,497 to Millar discloses a relatively short coupling structure (eg. 1 cm) slidably engaging the guidewire (see col. 3, lns. 14-17) allowing a plurality of diagnostic or therapeutic catheters such as sensor-carrying catheters which can be simultaneously coupled to a common guidewire (col. 1, lns. 15-22). Previously inserted devices need not be removed before insertion of subsequent devices.
Co-pending patent application Serial No. 07/859,769 to Buchbinder et al. discloses an over-the-wire catheter which provides support for the guidewire in multiple locations using rapid exchange loops along the catheter. Given the spacing of the rapid exchange loops, difficulties arise in threading the guidewire through them as each loop must be threaded individually. To facilitate threading the guidewire through the catheter rapid exchange loops, a loading attachment is needed. The guidewire loading attachment of the present invention is designed to snap on to the catheter shaft between pairs of such loops.